Profiling for perf tests

Profiling for perf tests

Stack profiling is quite useful and Linux ZFS test suite does not
current collect that data.

Linux perf is a common tool for this purpose though the perf record
data file can be quite large. With this change, Linux ZFS perf tests
capture perf record data if perf is installed on the system and
PERF_DO_PROFILING environment variable is set.

Reviewed by: John Wren Kennedy <jwk404@gmail.com>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Signed-off-by: Tony Nguyen <tony.nguyen@delphix.com>
External-issue: LX-971
Closes #7549